Separation cell and scavenger cell froths treatment

ABSTRACT

THE HOT WATER PROCESS FOR EXTRACTING BITUMEN FROM TAR SANDS PRODUCES A FROTH PRODUCT FROM A SEPARATION CELL. A SECONDARY RECOVERY MAY BE CONDUCTED ON THE MIDDLINGS FROM THE SEPARATION CELL TO PRODUCE ADDITIONAL FROTH WHICH USUALLY IS COMBINED WITH THE PRIMARY FROTH AND TREATED. IT HAS NOW BEEN FOUND THAT THE FROTH FROM THE SECONDARY RECOVERY OPERATION CAN BE UPGRADED IN BITUMEN CONTENT BY GRAVITY SETTLING. BY THE PROCESS OF THE PRESENT INVENTION THEN, SECONDARY RECOVERY FROTH IS SETTLED TO PRODUCE AN UPPER LAYER UPGRADED IN BITUMEN CONTENT OVER THE SECONDARY FROTH. THIS UPGRADED BITUMEN LAYER IS THEN ADDED TO THE PRIMARY FROTH FOR FURTHER PROCESSING.

July 20, 1 E. w. DOBSON 3,594,306

SEPARATION CELL AND SCAVENGER CELL FROTHS TREATMENT Filed April 3, 1967 TAR SANDS COMBINED WATER FROTH 2 I comomomwe DRUM 0:

0 LL I LU l- .l O I'- CC (I F- m 11- Lu (.9

w 5 SCAVENGER 9 FROTH CC 0 1 (I) E E A a. FROTH 2l SETTLER 5 OVERSIZE OIL-RICH MIDDLINGS l4 U SEPARATION ,ZONE FLOTATION i SCAVENGER Am ZONE MIDDLINGS '3 l0 OIL LEAN MIDDLINGS SAND TRAILINGS !.\"=QI..\T( )R.

ERNEST W. DOBSON ATTORNEY United States Patent US. Cl. 20811 4 Claims ABSTRACT OF THE DISCLOSURE The hot water process for extracting bitumen from tar sands produces a froth product from a separation cell. A secondary recovery may be conducted on the middlings from the separation cell to produce additional froth which usually is combined with the primary froth and treated. It has now been found that the froth from the secondary recovery operation can be upgraded in bitumen content by gravity settling. By the process of the present invention then, secondary recovery froth is settled to produce an upper layer upgraded in bitumen content over the secondary froth. This upgraded bitumen layer is then added to the primary froth for further processing.

BACKGROUND OF THE INVENTION (1) Field of the invention Tar sands, which are also known as oil sands and bituminous sands, are aggregates of sand, mineral and water impregnated with heavy petroleum. The largest and most important deposits of the sands are the Athabasca sands, found in northern Alberta, Canada. These sands underlay more than 13,000 square miles at depths of to 2000 feet. Total recoverable reserves after extraction and processing are estimated at more than 300 billion barrelsjust about equal to the world-wide reserves of conventional oil, sixty percent of which is in the Middle East. By way of comparison, the American Petroleum Institute estimated total United States oil reserves at the end of 1965 at 39.4 billion barrels.

The tar sands are primarily silica, having closely associated therewith an oil film. This oil varies from about 5 percent to 21 percent by weight, with a typical content of 13 weight percent of the total material. The oil is quite viscous6 to 8 API gravityand contains typically 4.5 percent sulfur and 38 percent aromatics.

In addition to oil and sand, the composition of the sands includes clay and silt in quantities of from about 1 to 50 weight percent, more usually 10 to 30 percent and a small amount of water in quantities of l to 10 percent by weight.

(2) Description of the prior art Several basic extraction methods have been known for many years for the separation of oil from the sands. In the so-called cold water method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.

In the hot water method, the bituminous sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of 240 to 210 F. The resulting pulp is dropped into a stream of circulating hot water and carried to a separation cell maintained at a temperature of about 150 to 200 F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step usually comprises aerating the middlings as taught by K. A. Clark, The Hot Water Washing Method, Canadian Oil and Gas Industries 3, 46 (1950).

It is the practice to combine these froths, dilute them with naphtha and centrifuge the diluted combination to remove more water and residual sand. The naphtha is then distilled off and the bitumen is coked to a high quality crude suitable for further processing. The present invention is directed to an improvement in the above described hot water process and more specifically is directed to a process for treating the separation cell and scavenger cell froths. The invention is :based on the discovery that the secondary recovery froth can be significantly upgraded in bitumen content by settling, thereby significantly reducing the water and mineral that must be separated in the subsequent centrifuging step.

It is particularly surprising that settling will upgrade the scavenger froth since the primary froth may not be so upgraded unless the froth emulsion is first broken by dilution and/ or added chemical aids. The scavenger froth need not be diluted or otherwise treated in order to bring about upgrading by settling.

SUMMARY OF THE INVENTION Generally, with the present invention, the froths from a hot water process are treated as follows:

The secondary froth which is the froth from the scavenger zone, is settled in a settling zone to form a lower layer of settler tailings substantially reduced in bitumen content compared to the secondary froth and an upper layer substantially upgraded in bitumen content compared to the secondary froth. The lower layer and the upper layer are separately removed from the settler and the upper layer is mixed with the primary oil froth. The primary oil froth is the froth product from the primary separation zone. The mixture of primary froth and product stream can then be further processed by, for example, dilution with a hydrocarbon diluent miscible with the bitumen in the mixture and capable of lowering its specific gravity and centrifuging to remove any remaining water and sand from the diluent-bitumen product.

In one embodiment of the present invention, the lower layer from the scavenger froth settler may be recycled and added to the oil-rich middlings from the primary separation cell for feed into the scavenger zone.

In the above described process in the settling step any type or combination of types of settlers may be used. For example, continuous mechanical thickeners or clarifiers consisting of a single-compartment cylindrical tank or basin with a sloping bottom, a conical central area over a discharge outlet, and rotating rakes that move the settled solids toward the center of the basin might be used. Tanks may be either square or rectangular when space is limited or when a vast amount of settling area, combined with a high volume of relatively dilute flow, is required.

Also in the above described process in the diluting step, any diluent may be used so long as it is a hydrocarbon capable of dissolving the bitumen constituent of the particular stream treated and of substantially lowering its specific gravity. While hydrocarbons such as benzene, xylene, toluene, gasoline, kerosene, furnace distillates or diesel fuels and others maybe used, petroleum naphtha is the preferred diluent.

BRIEF DESCRIPTION OF THE DRAWING The drawing schematically illustrates one embodiment of the present invention. The figure shows the process utilizing settling of the secondary froth to upgrade bitumen 3 content before addition to the primary froth preliminary to further treatment.

In the figure, bituminous tar sands are fed into the system through line 1 where they first pass to a conditioning drum or muller 16. Water and steam are introduced from 2 and mixed with the sands. The total Water so introduced is a minor amount based on the weight of the tar sands processed and generally is in the range of to 40 percent by weight of the mulled mixture. Mulling of the tar sands produces a pulp which then passes from the conditioning drum as indicated by line 3 to a screen indicated at 17. The purpose of screen 17 is to remove from the tar sands pulp any debris, rocks or oversized lumps as indicated generally at 4.

The pulp passes from screen 17 as indicated by 5 to a pump sump 18 where it is diluted with additional fresh water from 6 and a middlings recycle stream 7. The diluted pulp is then pumped via 8 to the primary separation zone 19. The settling zone in separator 19 is relatively quiescent so that all froth rises to the top and is withdrawn via line 9 while the sand settles to the bottom as a tailings layer which is wihdrawn through line 10.

A middlings layer which contains some oil that failed to separate is withdrawn from the cell through line 11 to a flotation scavenger zone 20. In this zone an air flotation operation is conducted to cause the formation of additional oil froth which passes from scavenger zone 20 through line 12 to a forth settler zone 21. An oil-lean water middlings stream is removed and discarded from the bottom of scavenger zone 20 via line 13.

In the settler zone 21, the scavenger froth forms into a lower layer of settler tailings which is withdrawn and recycled via 14 to be mixed with oil-rich middlings for feed to the scavenger zone 20 via line 11. In the settler zone an upper layer of upgraded bitumen froth forms above the tailings and is withdrawn through and mixed with primary froth from line 9 for further processing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Examples I through VIII The following table shows the results of several runs conducted on air flotation scavenger froth from a hot water process. In each run tar sands of varying composition were mulled with water, flooded and flushed into a separaion zone where a primary froth was formed and recovered. Oil-rich middlings were withdrawn from the settler and subjected to an air flotation to recover a secondary froth of the composition as indicated under the headings Secondary Froth. This secondary froth was removed and passed to a 150 gallon rectangular settler and was allowed to settle for the indicated residence times. A product was recovered from the settler and was determined to be of the composition indicated under Settler Product.

Secondary froth, wt.

percent:

Bitumen 24.0 23.2 7.2 12.3 9.8 9.2 11.4 9.3 Mineral 21.6 21.2 17.0 15.9 9. 2 12.4 0. 8 11.6 Water 54.4 55.6 75.8 71.8 81.0 78.4 78.8 79.1 Settler product, wt.

percent:

Secondary frotlL.-. 53 50 28 30 21 22 28 23 Bitumen 44.0 46.5 26.0 40.7 46. 5 42.6 41.7 40.6 Mineral 15.3 12.6 14.7 15.0 9. 1 12.8 17.2 13.8 Water 30.8 40.9 50.3 44.3 44.4 44.6 41. 1 45.6 Settler tailings, wt.

percent:

Bitumen 5.2 4.5 2.6 5.9 0.9 1.6 1.8 1.9 Mineral 27.2 28.1 17.5 16.2 5.0 12.1 14.3 14.5 Water 67.6 07.4 79.9 77.9 94.1 86.3 83.9 83.6 Settler residence time,

mlns 16.5 14 6 13 5 30.0 39.5 37.5 36.6 29.4

The data presented in the table show that froth from the scavenger cell can be upgraded to a product of substantially greater bitumen proportion than the secondary froth. It was noted that primary cell froth was not upgraded by settling under the same conditions.

What is claimed is:

1. In the hot water process for treating bitmuminous tar sands which comprises: forming a mixture of the bituminous sands and water, passing the mixture into a separation zone; settling the mixture in the separation zone to form an upper primary bitumen froth layer, a. middlings layer comprising water, mineral and bitumen and a sand tailings layer; separately removing the primary bitumen froth layer and the sand layer; passing a stream of middlings layer from said separation zone to an air flotation zone and therein recovering a secondary bitumen froth; the improvement which comprises:

(a) settling said secondary froth in the absence of a diluent in a settling zone to form a lower layer of froth settler tailings substantially reduced in bitumen content compared to said secondary froth and an upper product layer substantially upgraded in bitumen content compared to said secondary froth; and

(b) separately removing said lower layer of froth settler tailings and said upper product layer from said settling zone.

2. The process of claim 1 in which the lower layer of froth settler tailings from Step (b) is added to the stream of middlings layer from the primary separation zone as a recycle stream into said air flotation zone.

3. A method of treating at least a portion of the middlings from a separation zone in a hot water process for treating tar sands which comprises:

(a) passing said portion of middlings from said separation zone to an air flotation zone;

(b) recovering a secondary oil froth in said air flotation zone;

(c) settling said secondary froth in the absence of a diluent in a settling zone, to form a lower layer of froth settler tailings substantially reduced in bitumen content compared to said secondary froth and an upper product layer substantially upgraded in bitumen content compared to said secondary froth; and

(d) separately removing said lower layer of froth settler tailings and said upper product layer.

4. The method of claim 3, in which the layer of froth settler tailings from Step (d) is recycled and added to the middlings passing to the air flotation zone in Step (a).

References Cited UNITED STATES PATENTS 2,453,060 11/1948 Bauer et al. 208-11 2,968,603 1/1961 Coulson 208-11 3,401,110 9/1968 Floyd et a1 20811 FOREIGN PATENTS 741,303 8/1966 Canada 20811 488,928 12/1952 Canada 20811 491,955 4/1953 Canada 208-11 OTHER REFERENCES Report on the Alberta Bituminous Sands, by S. M. Blair, 1950, pp. 2630.

CURTIS R. DAVIS, Primary Examiner 

